Carpentry and Woodworking - How do you route sharp corners in a dado for shelf standards?

I guess this would be called a "stopped dado?" I want to add some shelf standards to a cabinet. I am going to route out a channel to set the standards flush. What I don't understand is how to get the ends to have sharp corners. The router bit is round, so I would expect a rounded end. If I was using a router table with a dado blade, I would expect to end up with a ramp at each end. Does this require chisling or something?

Use a flat bottom 3/4" router bit, stop short of the end of your run on each end. Cut the end of your shelf at the location of the end of the dado, the depth of the dado. Sort of a notch on each end that will sit flush to the sides of your cabinet. You won't know the dado is there. Not sure how you were using a rounded bit for a dado.

I think one of us does not understand the other (and it is quite possibly me that does not understand).

I have some existing cabinets that have shelf standards (not actual shelves, but the metal tracks that you can put clips in to support shelves. They looke exactly like this: http://www.rockler.com/rockler/images/57389-md.jpg). They are set flush into a dado. The groove that they sit in has perfect 90 degree corners (i.e. it is perfect rectangle). If I take a router, and cut a dado that stops short of exiting out the side, the end of the dado will be round. How do I get the right angle corners?

Nope, it was me. I was thinking you were dadoing in shelving, not shelf standards. My error. I use the appropriate sized (usually 3/4") bit in the router and the corresponding chisel on the ends. Actually I have a corner cutter for squaring off rounded door strike plate areas (http://www.rockler.com/product.cfm?page=1288&filter=corner). Just stop at the right length and chisel out the remaining part so it will fit flush. With the flat bit, all you will have to do is square off the corners. Hope this helped.